Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, a submersible pumping system includes a number of components, including an electric motor coupled to one or more pump assemblies. Production tubing is connected to the pump assemblies to deliver the wellbore fluids from the subterranean reservoir to a storage facility on the surface.
The wellbore fluids often contain a combination of liquids and gases. Because most downhole pumping equipment is primarily designed to recover liquids, excess amounts of gas in the wellbore fluid can present problems for downhole equipment. For example, the centrifugal forces exerted by downhole turbomachinery tends to separate gas from liquid, thereby increasing the chances of cavitation or vapor lock.
Gas separators have been used to remove gas before the wellbore fluids enter the pump. In operation, wellbore fluid is drawn into the gas separator through an intake. A lift generator provides additional lift to move the wellbore fluid into an agitator. The agitator is typically configured as a rotary paddle that imparts centrifugal force to the wellbore fluid. As the wellbore fluid passes through the agitator, heavier components, such as oil and water, are carried to the outer edge of the agitator blade, while lighter components, such as gas, remain close to the center of the agitator. In this way, modern gas separators take advantage of the relative difference in specific gravities between the various components of the two-phase wellbore fluid to separate gas from liquid. Once separated, the liquid can be directed to the pump assembly and the gas vented from the gas separator.
As shown in FIG. 1, prior art agitators typically include several straight blades 10 connected to a central hub 12. This agitator design is disclosed in U.S. Pat. No. 4,913,630 issued Apr. 3, 1990 to Cotherman, et al., U.S. Pat. No. 5,207,810 issued May 4, 1993 to Sheth and U.S. Pat. No. 4,901,413 issued Feb. 20, 1990 to Cotherman et al. Similar paddle designs are shown in U.S. Pat. No. 4,481,020 issued Nov. 6, 1984 to Lee et al. and U.S. Pat. No. 4,231,767 issued Nov. 4, 1980 to Acker. Despite the acceptance of this design, there are a number of drawbacks presented by the use of straight-blade agitator paddles. For example, straight-blade paddles tend to create significant turbulence in the fluid leaving the agitator. Straight-blade paddles also increase the load placed on the motor driving the gas separator.
There is therefore a continued need for an improved agitator design that more effectively and efficiently separates liquids from gases in a pumping system. It is to these and other deficiencies in the prior art that the present invention is directed.